fix: enable vision routing fallback in Path A describe

[codysk]

When the main model has vision:true (Path A), describe calls only used [llmConfig] and ignored the vision routing chain, so a main-model outage (e.g. kimi-k3 503) left vision describe dead with no fallback — placeholders instead of trying qwen3.7-plus etc.

Path A now uses dedupConfigs([llmConfig, ...visionLlmConfigs]): main model first, then the vision routing chain deduped by name (fallback to model@baseUrl fingerprint). Also pass the full vision chain (not [0]) from main.ts initializeCodeActExecutor to code-act-executor, widening its visionLlmConfig type to LLMConfig[].

src/core/vision-processor.ts      | 18 +++++++++++++++---
src/main.ts                       |  2 +-
src/subagent/code-act-executor.ts |  4 ++--
3 files changed, 18 insertions(+), 6 deletions(-)

This makes Path A describe consistent with the vision routing fallback already used by vision.see (host-call-handler) and Path B.